The present invention relates to an improved controller for street light applications, and more particularly to a radio navigation satellite system (RNSS) based street light controller that is adapted to be powered by a street light and control a street light lamp using a standard electrical interface on the street light.
Street light controllers are used throughout the world to control the operation of street light lamps. Desired properties of a street light controller include turning the lamp on nominally around dusk and turning the lamp off nominally around dawn. Variants of this control cycle that turn the lamp off at a predetermined time, such as midnight, are also known.
Many known street light controllers are photosensor based. Photosensor based street light controllers turn the street light lamp on and off based on a level of light detected by photosensors associated with the controller. More particularly, the controller turns the lamp off in response to the presence of sufficient light and turns the lamp on in response to the absence of sufficient light.
Photosensor based street light controllers experience a variety of problems. One is false positives. Light flashes detected by photosensors from, for example, stray automobile headlights or lightning can cause the lamp to turn off inadvertently. Once in the off state the lamp often remains there for a substantial time that depends on the restrike characteristics of the street lamp. Additionally, photosensor false positives reduce the life of the lamp due to the increased number of restrikes thereby increasing street light failure rates and total cost of ownership. Another problem is orientation. Photosensor based street lights must generally be positioned to capture ambient light and to meet other requirements of the application, topography and photosensor type. Another problem is drift. Photosensor based street light controllers often experience drift due to photo cell aging that causes lamp on/off times to deviate from schedule. High heat in photo cells often accelerates drift. Yet another problem is atmospheric conditions. Atmospheric conditions such as pollution and cloud cover often affect performance of photosensors. Moreover, different photosensor types react to atmospheric conditions differently. For example, Si photosensors are extremely sensitive to infrared light which often necessitates installation of infrared blocking glass filters in conjunction with such photosensors. Yet another problem is night control. Electronic timers or secondary switching mechanisms must generally be employed in applications that require photosensor based street lights to be turned off during the night. Yet another problem is hysteresis. Photosensor based street light controllers must generally account for the effects of hysteresis in order to accurately coordinate on/off state with dusk and dawn. Yet another problem is power draw. Photosensors consume substantial power which proves expensive over the life span of the street light controller.
Despite these problems, photosensor based street light controllers are popular because they have a generally low upfront cost, require little user configuration, conform to industry standard form factors for street lights and are adapted to be plugged into an American National Standards Institute (ANSI) standard electrical interface configured on most street lights. These characteristics have generally enabled photosensor based street light controllers to be deployed on a one-per-light basis, which has simplified street light wiring, and enabled plug-and-play replacement in the event of failure. It would therefore be desirable to reduce problems associated with photosensor based street light controllers while maintaining positive characteristics of these controllers.
Meanwhile, it is known to use RNSS receivers, such as global positioning system (GPS) receivers, in street light control systems. In known RNSS based street light control systems, the GPS receiver generally does not conform to a standard form factor for individual street lights but rather is adapted for mounting to a pole to control multiple street lights simultaneously. Known RNSS based street light control systems are not pluggable into the ANSI-standard electrical interface configured on most street lights but instead rely on wiring terminals for electrical connectivity with multiple street lights. Moreover, since a single controller is adapted to control a large number of street lights, a system-wide failure occurs if the controller fails. Furthermore, known RNSS based street light control systems typically require significant user input to obtain desired configuration and operation.